Authorities are unsure where the child was exposed to the potentially deadly disease. Picture: SuppliedSource:Supplied

The disease, caused by the bacterium Yersinia pestis, is often associated with the “Black Death” epidemic that was spread by rats and killed millions in medieval Europe. This strain of bacteria still occurs naturally in some rodent populations, spread by fleas in rats and squirrels, but is exceedingly rare in humans.

Occasionally some humans do get infected with Yersinia pestis, usually through a flea or animal bite, according to Health.com. Person-to-person transmission is extremely rare, and wasn’t a factor in this case, officials said.

The last urban plague epidemic in the US happened in Los Angeles in 1924, when 30 people died, and since then, the disease has been scattered in rural areas on the west side of the country.

Since 1990, there have been two cases of plague in humans in Idaho and eight in Oregon.